1. Field of the Invention
The present invention relates to zirconia ceramic articles and to a method for manufacturing the same.
2. Description of the Prior Art
It is known to use zirconia ceramic articles for various applications requiring strength or wear resistance at elevated temperatures. Specifically, zirconia ceramics comprising mainly zirconia (ZrO.sub.2) and yttrium oxide (Y.sub.2 O.sub.3) are conventionally used for this purpose.
In the use of zirconia ceramic articles of this type, it is important that the article be resistant to cracking, particularly in the presence of thermal shock to which these articles are typically subjected in high temperature applications. With conventional zirconia ceramic articles, a major source of crack initiation results from microstructural heterogeneities, which may be in the form of inclusions resulting during production of the particulate material from which the article is produced. Specifically, inclusions and impurities are produced in the particle mass during conventional ball milling. Incident to the manufacture of ceramic articles the material is ball milled to achieve fine particle size prior to compacting and sintering to achieve the desired dense article.
In addition, crack initiation may result from chemical inhomogeneity resulting from incomplete diffusion and large crystal size caused by prolonged sintering times at elevated temperature required to achieve complete sintering.
Resistance to crack propagation may be achieved in ceramic articles of this type by providing an increased content of metastable tetragonal crystalline phase. During conventional preparation of these ceramic articles, however, significant transformation of the this desirable metastable phase to the monoclinic phase occurs. This results in decreased resistance to crack propagation.